1. Field of the Invention
The present invention relates generally to bandsaw machines having a flexible bandsaw blade trained around a plurality of wheels or pulleys to perform cutting operations and, more particularly, pertains to methods and apparatus for detecting the cutting resistance in bandsaw machines.
2. Description of the Prior Art
The prior art concerning the present invention will be described, by way of example, about what is called a horizontal bandsaw machine, although the present invention is applicable not only to horizontal bandsaw machines but also to vertical bandsaw machines.
As is well known, horizontal bandsaw machines comprise a base on which a workpiece or workpieces to be cut are placed and clamped and a cutting head assembly in which a flexible endless bandsaw blade is trained around a pair of wheels or pulleys, one of which is power driven to drive the bandsaw blade. In the cutting head assembly, the bandsaw blade is slidably held and guided with its cutting edge faced perpendicularly downwardly by a pair of guide means at the cutting zone where cutting is performed so that it may cut into the workpiece. The cutting head assembly is so arranged as to be raised away from and lowered toward the base by a suitable means such as a hydraulic motor around a hinge pin or along one or more vertically disposed guide means. Thus, in each cutting cycle, the cutting head assembly is first raised and then lowered towards the base so as to enable the bandsaw blade being driven therein around the wheels to cut the workpiece which has been placed and clamped on the base. Also, in automatic horizontal bandsaw machines, there are provided arrangements for automatically raising and lowering the cutting head assembly and automatically feeding workpieces to be cut into the cutting zone after completion of each cutting cycle.
In such horizontal bandsaw machines, it is desired to feed the bandsaw blade into the workpiece to be cut always at an optimum feeding speed with an optimum feeding force in order to perform an efficient cutting operation with a high cutting accuracy without decreasing the life of the bandsaw blade. For this purpose, it is necessary to control the feeding speed and force of the bandsaw blade during a cutting operation by accurately detecting the cutting resistance with which the bandsaw blade will meet.
It has been customary that the cutting resistance of the bandsaw blade is detected by obtaining the back pressure which will occur during a cutting operation in the hydraulic cylinder for raising and lowering the cutting head assembly holding the bandsaw blade. In this method, the force applied to the bandsaw blade during the cutting operations is detected as a normal component of the cutting resistance based upon the difference between the back pressure of the hydraulic cylinder in cutting operation and that out of cutting operation. In this conventional method, however, it has been impossible to detect momentary changes in the cutting resistance during a cutting operation, and it is only possible to obtain an average cutting resistance, since the normal component of the cutting resistance on the bandsaw blade is indirectly obtained at a position away from the cutting zone of the bandsaw blade. Although various attempts have been made to detect the cutting resistance in bandsaw machines, it has been conventionally impossible to control the feeding speed and force in immediate response to changes in the cutting resistance.